Bonding Gas Supply in an Outbuilding

[davesparks]

Read my text. I'm querying the sub-main earth size, not main bonding.

If main bonding is required at the outbuilding, which in this case it is, then the submain cpc also is a main bond and so must meet the 10mm requirement.

 

[davesparks]

Can you not utilise the armourings along with the third core to increase your effective CPC csa ?

You might find it complies after all if this has already been done, I will have a look through the various tables later.

Otherwise just note it on the EICR as per the advice given in the links above

No, the main bond is required to be a single conductor and cannot be made up of smaller conductors combined

 

[TJ Anderson]

No, the main bond is required to be a single conductor and cannot be made up of smaller conductors combined

I'm not aware of anything requiring single conductor only in BS7671. Where does is stipulate this?

 

[spark 68]

No, the main bond is required to be a single conductor and cannot be made up of smaller conductors combined

I'm not aware of anything requiring single conductor only in BS7671. Where does is stipulate this?

I think Dave is referring to reg 543.2.5

Even so, taking 543.2.5 into account, one of my tables for Equal Size Conductor Cables PVC ins. SWA to BS3646, operating at 70 degrees C gives the equivalent copper csa of the armourings for 3 core 6mm[SUP]2[/SUP] SWA as 15mm[SUP]2[/SUP]
If that's the case then the armourings satisfy as a MPB and the 3rd core as the CPC.

 

[TJ Anderson]

I think Dave is referring to reg 543.2.5

Even so, taking 543.2.5 into account, one of my tables for Equal Size Conductor Cables PVC ins. SWA to BS3646, operating at 70 degrees C gives the equivalent copper csa of the armourings for 3 core 6mm[SUP]2[/SUP] SWA as 15mm[SUP]2[/SUP]
If that's the case then the armourings satisfy as a MPB and the 3rd core as the CPC.

543.2.1

(I have quoted the relevant sub sections)

A protective conductor may consist of one or more of the following

(ii) A conductor in a cable
(v) A metal covering, for example, the sheath. screen or armouring of a cable

Going by that, you could use the combination of armour sheath and cable conductor as a main protective bonding conductor.

 

[spark 68]

543.2.1

(I have quoted the relevant sub sections)

A protective conductor may consist of one or more of the following

(ii) A conductor in a cable
(v) A metal covering, for example, the sheath. screen or armouring of a cable

Going by that, you could use the combination of armour sheath and cable conductor as a main protective bonding conductor.

If you look at 543.2.5 though, this refers specifically to the sheath as a protective conductor and must fulfill condition (i) or (ii) of the reg you quoted, I read this that the sheath must be able to satisfy one of the functions of a given protective conductor in it's own right.

If it does, then we can use the 3rd core as another protective conductor, be that a MPB or a CPC, thus utilizing the other parts of the reg 543.2.1

Now the particular table I looked at gives the copper equivalent of a 6mm PVC 3-core swa as 15mm, now normally we use a rule of thumb that steel has 8X less the conductivity of copper size for size, but this depends on the K values used, this I would need to calculate properly to see if that particular table is true.

Edit: what 543.2.5 is basically saying is that you cannot split the function of a given single protective conductor between the sheath and a core, but we could use the sheath as one protective conductor if it complies as such, and the core as another protective conductor likewise so long as it also complies as another protective conductor.

In this particular case we could possibly use the sheath as the MPB, and the 3rd core as the CPC, it might be the case that in another situation it could be the 3rd core as the MPB and the sheath as the CPC.

 

[Silly Sausage]

Chaps, I'll just bring your attention to the fact that 543 applies to Protective Conductors only, NOT Protective Bonding Conductors, that's 544.

 

[spark 68]

Chaps, I'll just bring your attention to the fact that 543 applies to Protective Conductors only, NOT Protective Bonding Conductors, that's 544.

I don't think that matters in this context Archy, the general rules for protective conductors in 543 apply equally to section 544.

Section 544 applies additional conditions regarding minimum sizes to the preceding section, more specifically to bonding conductors.

 

[Engineer54]

If you look at 543.2.5 though, this refers specifically to the sheath as a protective conductor and must fulfill condition (i) or (ii) of the reg you quoted, I read this that the sheath must be able to satisfy one of the functions of a given protective conductor in it's own right.

If it does, then we can use the 3rd core as another protective conductor, be that a MPB or a CPC, thus utilizing the other parts of the reg 543.2.1

Now the particular table I looked at gives the copper equivalent of a 6mm PVC 3-core swa as 15mm, now normally we use a rule of thumb that steel has 8X less the conductivity of copper size for size, but this depends on the K values used, this I would need to calculate properly to see if that particular table is true.

Edit: what 543.2.5 is basically saying is that you cannot split the function of a given single protective conductor between the sheath and a core, but we could use the sheath as one protective conductor if it complies as such, and the core as another protective conductor likewise so long as it also complies as another protective conductor.

In this particular case we could possibly use the sheath as the MPB, and the 3rd core as the CPC, it might be the case that in another situation it could be the 3rd core as the MPB and the sheath as the CPC.

Not sure what table you're looking at, but there is no way 15 mm of steel armour is going to be the equivalent conductance of 6mm copper, no matter what K values are being applied...

A typical CSA of wire armouring for a typical 3 core 6mm SWA cable is 23mm, and requires minimum of 13.6mm for the SWA to comply for CPC compliance...

Agree you cannot combine different CPC conductors of different materials, both conductors must be able to fulfil compliance in it's own right.

Where PME applies, (when bonding is required) the minimum size of 3 Core SWA would need to be 10mm. That by the way, requires a minimum 22.6mm CSA of of steel wire to meet just the cables CPC requirements... Typically it has a CSA of 39mm of steel wire armour...

 

[spark 68]

Not sure what table you're looking at, but there is no way 15 mm of steel armour is going to be the equivalent conductance of 6mm copper, no matter what K values are being applied...

A typical CSA of wire armouring for a typical 3 core 6mm SWA cable is 23mm, and requires minimum of 13.6mm for the SWA to comply for CPC compliance...

Agree you cannot combine different CPC conductors of different materials, both conductors must be able to fulfil compliance in it's own right.

Where PME applies, (when bonding is required) the minimum size of 3 Core SWA would need to be 10mm. That by the way, requires a minimum 22.6mm CSA of of steel wire to meet just the cables CPC requirements... Typically it has a CSA of 39mm of steel wire armour...

No, the copper equivalent was given as 15mm in one table I looked at.

I appreciate that particular table maybe incorrect, and I would need to do the calcs properly, actually I think I got the table from here

If the k values in that table are correct then the armourings could be used as the MPB, with the 6mm core used for the CPC part.

I will attach the table here for you to look at., the figure in (I think it is brown or orange is the copper equivalent)

If I get my paper work finished I will have a closer look at the calcs used.

 

[Engineer54]

Agggggh!! Not that poxy Wirenut table again!! Do yourself a favour spark 68 (and anyone else that still has this table) throw that bloody thing in the bin where it has belonged for years!!

There is very little in that table i would take as correct, the whole thing about this table, is it's inconclusive, misleading and in many respects just plain Wrong!!!

Just get shot of the bloody thing!!

 

[davesparks]

Chaps, I'll just bring your attention to the fact that 543 applies to Protective Conductors only, NOT Protective Bonding Conductors, that's 544.

So what does a section title protective conductors apply to? If it's not protective bonding conductors then it also can't be circuit protective conductors.

 

[spark 68]

Agggggh!! Not that poxy Wirenut table again!! Do yourself a favour spark 68 (and anyone else that still has this table) throw that bloody thing in the bin where it has belonged for years!!

There is very little in that table i would take as correct, the whole thing about this table, is it's inconclusive, misleading and in many respects just plain Wrong!!!

Just get shot of the bloody thing!!

Cheers, E54

TBF I thought that table was a little on the optimistic side ,it is the only one I have that shows the copper equivalent, I have others that show which sizes the SWA are suitable for use as a CPC, I probably got one of those from you.

When I have finished my paperwork I might have a go at the calcs for the hell of it , the OP should really be looking at this, but then again he could just C3 it, if it is not showing any distress etc..etc..

Note to self, do paperwork as and when it comes in, instead of leaving it all to the last minute! lol

 

[GEOFF S]

543.2.1

(I have quoted the relevant sub sections)

A protective conductor may consist of one or more of the following

(ii) A conductor in a cable
(v) A metal covering, for example, the sheath. screen or armouring of a cable

Going by that, you could use the combination of armour sheath and cable conductor as a main protective bonding conductor.

I agree, i see no issues.

Cheers

 

[spark 68]

I agree, i see no issues.

Cheers

I disagree, and there are issues, see 543.2.5

 

[GEOFF S]

I disagree, and there are issues, see 543.2.5

I dont have the regs to hand, could you expand?

Cheers

 

[Leesparkykent]

K1/k2xS=13.5294

k1=115
k2=51
S= 6mm

 

[GEOFF S]

Thanks Lee.

Well i still see no issues.

Cheers

 

[spark 68]

I dont have the regs to hand, could you expand?

Cheers

Then why the blanket statement ?

543.2.5 The metal covering including the sheath (bare or insulated) of a cable, in particular the sheath of a mineral insulated cable, trunking and ducting for electrical purposes and metal conduit, may be used as a protective conductor for the associated circuit, if it satisfies both requirements of items (i) and (ii) of reg 543.2.2

543.2.2 this reg is actually more about switchgear and bus bar trunking etc. but the salient points here are (i) and (ii)

(i) Its electrical continuity shall be assured, by construction or by suitable connection, in such a way as to be protected against mechanical, chemical or electrochemical deterioration.

(ii) Its cross sectional area shall be at least equal to that resulting from 543.1, or verified by test in accordance with the appropriate part of BSEN 61439 series.


What this is basically saying is that if the armouring is of insufficient csa to satisfy its use as a protective conductor, you cannot make up the difference with another undersized protective conductor, either the armouring has to comply on its own for its intended purpose, or the other protective conductor has to comply the same way. as an example of what would not be allowed, consider you need a CPC of say 10mm, and you calculate your armouring works out as a copper equivalent of 6mm, you cannot just add another CPC or core of 4mm to make up the difference, you would need the additional CPC or core to be 10mm on its own.

You can use both where for instance the armouring would comply as a CPC and a core for the MPB purposes, or vice versa.
This is one reason why you sometimes see a 10mm G/Y cable running along side an armoured cable.

 

[Leesparkykent]

SWA, armour equivalent copper - Ted